Bone cement mixing and loading apparatus

ABSTRACT

An apparatus for mixing bone cement and containing the mixed bone cement preparatory to dispensing. The mixing chamber has an outlet for the mixed cement. A cartridge has an inlet releasably coupled to the outlet of the mixing chamber for receiving mixed bone cement therefrom. Structure is provided for moving cement from an upper region of the mixing chamber down into a lower region thereof to mix same and for moving such mixed cement off an inner surface of the mixing chamber and into the cartridge.

This application is a divisional of U.S. Ser. No. 07/769 004 filed Sep.30, 1991, now U.S. Pat. No. 5,265,956, and a continuation of U.S. Ser.No. 08/132 031 filed Oct. 5, 1993, now abandoned, in turn a divisionalof above-mentioned U.S. Ser. No. 07/769 004 filed Sep. 30, 1991, nowU.S. Pat. No. 5,265,956.

FIELD OF THE INVENTION

This invention relates to an apparatus for mixing and loading a two-partbone cement of a type suitable for fixing a prosthesis to bone in asurgical patient, and more particularly to such an apparatus for mixingand loading such cement under a partial vacuum (subatmosphericpressure).

BACKGROUND OF THE INVENTION

In orthopedic procedures it is common to use an acrylic bone cement toaffix a prosthesis to the bone, for example a hip joint implant to theinterior surfaces of the femur. Typically such bone cements arecomprised of a liquid monomer and a solid polymer. The solid polymercontains the reaction initiator and is typically a finely dividedpowder. When the liquid monomer contacts the polymer, a reaction ensuesthat polymerizes the monomer and cross links the polymer into a highmolecular weight polymeric solid. It is known that when the monomer andpolymer are mixed under a partial vacuum, the void volume (portion ofthe volume occupied by air or other gas bubbles) of the resultant highmolecular weight polymeric solid is advantageously considerably lessthan when mixed in air at atmospheric pressure.

Resulting bone cements of this type have been applied to the surgicalsite in a variety of ways. One way is to use an extrusion device broadlysimilar to a caulking gun. Typically in prior devices, the mixed bonecement is transferred to a cylindrical cartridge in air at atmosphericpressure or is mixed in the cartridge itself under a partial vacuum.Transfer of the cement into the cartridge in air at atmospheric pressureallows the incorporation of air into the mixture and thus unfortunatelycan increase the porosity of the cement. On the other hand, when thecement is mixed within the cartridge itself, the surface area availableto remove the air from the mixture under partial vacuum is not optimal.

Accordingly, the objects and purposes of the present invention includeprovision of apparatus intended to overcome these and other drawbacks ofprior systems.

A further object of the present invention is to provide adequate surfacearea to remove air during the mixing process and to transfer the mixedcement into the cartridge while under a partial vacuum.

One aspect of the invention involves an apparatus for mixing bone cementand containing the mixed bone cement preparatory to dispensing, theapparatus comprising a mixing chamber having an outlet for mixed cement,a cartridge having an inlet releasably coupled to the outlet of themixing chamber for receiving mixed bone cement therefrom, and means formoving cement from an upper region of the mixing chamber down into alower region thereof to mix same and for moving such mixed cement off aninner surface of the mixing chamber and into the cartridge.

Other objects and purposes of the invention will be apparent to personsacquainted with apparatus of this general type upon reading thefollowing description and inspecting the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a pictorial view of a mixing and loading apparatus embodyingthe invention, with its lid assembly removed from atop the mixingchamber;

FIG. 2 is an exploded pictorial view of the apparatus of FIG. 1 butincluding the lid assembly, and a cartridge to be loaded with bonecement and an example of an outlet nozzle alternatively securable to thecartridge;

FIG. 3 is an enlarged central cross-sectional view of the FIG. 2apparatus with the piston and push rod in their upper (preloading)positions;

FIG. 3A is an enlarged fragment of FIG. 3 showing the piston at thelower end of the funnel;

FIG. 3B is an enlarged fragment of FIG. 3 showing the seal between thelid assembly and the top of the funnel;

FIG. 3C is an enlarged fragment of FIG. 3 showing the seal between thefunnel and the vacuum shroud;

FIG. 4 is a view similar to FIG. 2 but with the piston and push rod inrespective downward positions;

FIG. 5 is an enlarged side elevational view of the shaft assembly,substantially as taken along the line 5--5 of FIG. 2 and showing sameedgewise;

FIG. 5A is a fragmentary enlarged central cross-sectional view of theshaft assembly substantially taken on the line 5A--5A of FIG. 4 and withthe crank handle rotated 90° clockwise as seen from the top of FIG. 4,and with the push rod removed;

FIG. 5B is a bottom view of the shaft assembly substantially taken onthe line 5B--5B of FIG. 5;

FIG. 5C is a view similar to FIG. 5A but with the push red in place; and

FIG. 6 is an exploded pictorial view of the cover and rotor portions ofFIG. 2.

FIG. 7 is an enlarged fragmentary top view of the FIG. 4 auger takenfrom the top of the auger and showing its outer edge contact with theinner surface of the funnel.

DETAILED DESCRIPTION

A bone cement mixing and loading apparatus 10 (FIGS. 1 and 2) embodyingthe invention comprises a mixing chamber 11 and a cartridge 12 locatedbelow the mixing chamber 11 for receiving mixed bone cement therefrom. Avacuum shroud 13 (FIG. 3) supports the mixing chamber and cartridge ashereafter discussed.

The vacuum shroud 13 comprises an upstanding cylindrical casing 20having a closed bottom 21. The bottom portion of the casing 20 has adownwardly and outwardly flared, substantially conical, skirt 22. Theskirt 22 preferably protrudes slightly below the casing 20. The bottomedge 23 of the skirt 22 supports the apparatus 10 on a table or the likeduring mixing and loading. Preferably the diameter of the skirt 22 is atleast approximately equal to the maximum diameter of the mixing chamberto support same in a stable manner and to minimize the effect ofhorizontal moments upon the apparatus 10 during use.

The upper end of the vacuum shroud casing 20 is open upward andsurrounded by a circular radial flange 24. The center line of theoutside diameter of the radial flange 24 is not coaxial with thecylindrical casing 20 but rather is offset sidewardly (to the right inFIG. 3). In the embodiment shown, the rightward (FIG. 3) portion of theradial flange 24 extends to the right about as far as the widest pointon the mixing chamber 11. A flat, resilient, annular seal ring 25 seatsatop the radially outer portion of the radial flange 24 and is laterallyfixed by a perimeter ridge 26 fixedly upstanding from the perimeter ofthe radial flange 24. A depression 27 in the top of the radial flange 26extends radially inward from the seal 25 to communicate with the top ofthe cylindrical casing 20.

The mixing chamber 11 comprises an open-topped, downwardly convergingfunnel 30 (FIGS. 2 and 3) whose sidewall is of frusto-conical shapeintermediate its upper and lower ends and through the major portion ofits height. In the preferred embodiment shown, the frusto-conicalsidewall 31 of the funnel 30 is angled divergently upwardly at about 15°to 25° (here about 20°) to the vertical. A radial flange 32 extendsfixedly and horizontally outward from the frusto-conical sidewall 31 ofthe funnel 30, adjacent but spaced above the lower end of such sidewall31. The flange 32 is annular and surrounds the bottom portion of thefunnel 30 but is eccentrically offset to the right thereof in FIGS. 2and 3, in the same manner as the radial flange 24 on the top of thevacuum shroud 13. The funnel flange 32 is sized and located laterally toseat in a circumferentially continuous manner on the seal ring 25. Theupper portion of the perimeter ridge 26 of the vacuum shroud 13 closelysurrounds the funnel flange 32 to positively locate it horizontally, andradially about the central axis of the funnel 30.

The upstanding central axis of the funnel 30 and the upstanding centralaxis of the vacuum shroud cylindrical casing 20 are coaxial, as seen inFIG. 3, when the funnel flange 32 is properly seated on the seal ring 25and vacuum shroud radial flange 24.

An upstanding web 34 extends rightward from the funnel 30 (as seen inFIG. 2 and 3) and extends upward from the top of the flange 32. Theupstanding radially outer edge 35 of the web 34 is thickened and housesa fluidic communicative passage 36 which is open at its bottom to thedepression 27 and is open at its top flush with the top of the funnel30. The opening of the passage 36 is larger at the top of the funnel 30than at its bottom which leads to the depression 27. This creates afluidic restriction at its bottom 27 which creates a pressure drop. Thispressure drop in turn forces the conical mixing chamber to be vented toatmospheric pressure before the shroud. As partially seen in FIG. 2 andindicated by broken lines in FIG. 3, a hollow stub 37 communicates withthe passage 36 intermediate its ends for connection thereto of a vacuumtube 38 leading through an activated carbon filter 40 to a conventionalvacuum source VS.

In the embodiment shown, the top of the funnel 30 has a relatively shortcylindrical top portion 41 extending up from the conical sidewall 31 andsurrounded by a horizontal radially outward extending annular flange 42.The vertical passage 36 opens up through the top of the annular flange42, leaving a hole 43 in the top of the flange. The flange 42 ispreferably coaxial with the funnel 30.

A lid assembly 44 includes a lid 45 including a horizontal wall 46(FIGS. 2 and 3) having an upstepped perimeter 47 bounded by acylindrical perimeter flange 50 having portions extending both above andbelow the horizontal wall 46 and upstepped perimeter 47. The dependingportion of the perimeter flange 50 and upstepped perimeter 47 cooperatewith the funnel top flange 42 to trap therebetween a resilient vacuumseal ring, here an O-ring, 51. The bottom portion of the cylindricalperimeter flange 51 snugly but vertically slidably surrounds the funneltop flange 42 to prevent sideways displacement of the lid assembly 44with respect to the funnel 30.

A cylindrical hub is fixedly upstanding from the top of the horizontalwall 46 of the lid in coaxial relation therewith, as seen in FIGS. 3 and6. Platelike spokes 53 (FIGS. 2 and 6) radiate from the hub 52 out tothe perimeter flange 50 to increase the rigidity of the horizontal wall46 of the lid 45.

The hub 52 vertically and rotatably supports a hollow shaft assembly(FIGS. 3 and 6) pendent coaxially therefrom. The shaft assembly 54depends into the funnel 30 when the lid assembly 44 closes the top ofthe funnel 30 as seen in FIG. 3. The shaft assembly 54 in turn coaxiallyslidably supports therein a push rod 55. Seals 65 and 106 hereafterdescribed are interposed between the hub 52, shaft assembly 54 and pushrod 55 to prevent air leakage therepast into the funnel 30.

The shaft assembly 54 (FIG. 6) comprises a hollow tubular head 60 (FIG.6) from which fixedly and coaxially depends a rigid tube 61. The head 60has an up-opening bore 59 (FIG. 5A) which steps down to a downwardopening coaxial reduced diameter bore 59A which in turn fixedly receivescoaxially therein the upper end of the rigid tube 61. A rotor 62 isfixed on the lower end of the tube 61.

The head 60 (FIGS. 5A and 6) includes a generally cylindrical upperportion 63 rotatably supported within the lid hub 52. An annular groove64 low on the cylindrical upper portion 63 receives a resilient annularseal, here an O-ring, 65 which bears sealingly on the interior of thelid hub 52 and creates a vacuum tight seal between the shaft assembly 54and lid 45 to prevent passage of air therepast into the mixing chamber11. A radially outwardly extending annular flange 66 at the bottom ofthe cylindrical upper portion 63 of the head bears on the underside ofthe horizontal wall 46 of the lid 45 to block upward motion of the shaftassembly 54 with respect to the lid 45.

A manually rotatable crank handle 70 (FIG. 5A) is fixed to the top ofthe shaft head 60 and rests atop the lid hub 52 to prevent the shaftassembly 54 from dropping downward with respect to the lid 45. Moreparticularly, the handle 70 includes an upstanding hollow boss 71 at oneend thereof which telescopes over the top of the head 60. The boss 71has a central through opening 72 which receives the upper end of thehead 60. Circumferentially spaced, radially outwardly hooked fingers 73at the upper end of the head 60 are resiliently radially outwardlybiased The outwardly hooked fingers 73 snap over an upward facingannular step 74 located in and near the top of the central throughopening 72 of the handle boss 71, to prevent the handle 70 from beinglifted off the top of the shaft head 60. The bottom of the handle boss71 rests rotatably atop the lid hub 52 so as to prevent the shaftassembly 54 from dropping down through the lid 45. In this way the shaftassembly 54 is rotatably supported by the lid 45 and is axially fixedwith respect thereto.

The handle boss 71 has a downward facing step 75 spaced below the step74 and which rests rotatably atop the generally cylindrical upperportion 63 of the shaft head 60. Thus, the handle is vertically fixedbetween the top of the generally cylindrical upper portion 63 of thehead and the radially outwardly hooked fingers 73 spaced thereabove.

The end of the crank handle remote from the handle boss 71 rotatablysupports an upstanding, hand engageable knob 78 orbitable to rotate theshaft assembly 54.

Rotation of the handle 70 positively rotates the shaft assembly 54. Inthe embodiment shown, this is accomplished by bearing of a pair ofdiametrally opposed flats 76 within the lower portion of the handle bossthrough opening 72 on a corresponding pair of diametrally opposed flats77 (FIGS. 5 and 6) on the upper part of the generally cylindrical upperportion 63 of the head 60.

The shaft assembly head 60 (FIG. 5A) includes a coaxial stepped tubularskirt 80 (FIGS. 5A and 6) which extends below the flange 66 and hencebelow the lid 45. The skirt 80 is thus located within the mixing chamber11 when the lid assembly and shaft assembly are located atop the funnel30 in the normal position of use shown in FIG. 3. The rigid tube 61(FIG. 5A) is fixedly telescoped at its upper end in the lower portion ofthe skirt 80 for rigid coaxial depending fixation of the tube 61 to thebottom of the head 60.

The rotor 62 is fixed to the bottom of the tube 61 and comprises anauger 81 (FIGS. 5A and 6), a paddle 82 and a base 83 interconnecting theauger 81 and paddle 82 to the bottom of the tube 61 in a rigid manner.

As seen in FIG. 3, the base 83 extends down to about the bottom of theconical sidewall 31 of the funnel 30. The auger 81 and paddle 82 extendgenerally upward from the base 83 into the midportion of the funnel 30.The auger 81 extends up to substantially the top of the conical sidewall31 and the paddle 82 extending to about half that height. As seen inFIGS. 5, 5B and 6, the auger 81 and paddle 82 are inclined upward inopposite directions away from the diametral plane 84 (FIG. 5B) of thebase, here at about 25° and 15° respectively, as seen in FIG. 5.

The auger 81 and paddle 82 are thin platelike elements of truncatedtriangular perimeter shape (the bottom point of the triangle being cutoff in each instance). As seen in FIG. 3, the auger 81 and paddle 82have generally upstanding radially inner edges 85 and 86 respectively(FIGS. 3 and 5B) which lie in planes parallel to the upstandinglongitudinal axis of the shaft tube 61, and are respectively radiallyspaced from and radially closely adjacent to the tube 61. The auger 81and paddle 82 have generally upstanding radially outer edges 91 and 92respectively, which angle up and out substantially at the same angle asthe upward and outward angling conical sidewall 31 of the funnel 30. Theauger outer edge 91 bears (as most easily seen in FIG. 7) against thefunnel sidewall 31 to wipe therealong in response to rotation of thehandle 70. On the other hand, the outer edge 92 of the paddle 82 isspaced radially inward from the funnel sidewall 31. In the preferredembodiment shown, the top edges 93 and 94 of the auger 81 and paddle 82are substantially horizontal.

Whereas the paddle 82 is solid, the auger 81 has a large central opening95 (which indeed here is bigger than the paddle 82). The auger centralopening 95 has edges which are approximately parallel, and are inwardlyspaced from the top, bottom and side perimeter edges (e.g. 93, 85 and91) of the auger 81.

In the embodiment shown, the base 83 and paddle 82 are integrally moldedof a suitable rigid plastics material, whereas the auger 81 is ofsubstantially rigid, but elastically bendable, stainless steel sheetmaterial with its bottom end portion fixed in a slot 96 (FIG. 5) in thebase 83. In the preferred embodiment shown, the auger is insert moldedto the base 83. The auger is rigidly fixed by plastic flowing throughholes in the auger and solidifying as seen at 97. The central opening 95in the platelike auger 81 makes the auger 81 more flexible and alsoincreases the number of edges engageable with cement components to bemixed so as to increase the amount of mixing per rotation of the handle.

The radially outer edge 91 of the preferred auger 81 shown is, in therelaxed planar condition of the auger, straight. On the other hand, withthe plane of the auger tilted at 25° to a diametral plane of the funnel30, the line of intersection of the plane of the auger with the interiorsurface of the conical funnel sidewall 31 would be curved. However, theflexibility of the sheet material of the auger 81 allows it to bend andthereby define a curved, rather than planar, sheet as it rotatably mixescement within the funnel 30. The curvalinear bending of the sheetmaterial of the auger 81 accordingly causes the radially outer edge 91thereof to be similarly curvalinearly bent, so that the auger radiallyouter edge 91, along its entire height, closely engages the interiorsurface of the conical sidewall 31 of the funnel 30 to wipe cementtherefrom.

The push rod 55 (FIGS. 3, 5C and 6) comprises a circular cross section,cylindrical rod element 100. The push rod 55 fixedly, coaxially tops therod element 100 with a head 101 comprising a shank 102 fixed on theupper end of the rod element 100 and topped by a fixed, integral andradially outwardly extending, hand depressible button 103. The shank 102has upper and lower annular grooves 104 and 105 (FIGS. 5C and 6),respectively near the mid-portion thereof and near the lower endthereof. The push rod is installed in the hollow shaft assembly 54 byinserting the lower end of the rod element 100 downward into theup-opening bore 59 (FIG. 5A) of the head 60.

The push rod 55 has first and second operating positions (respectiveupper and lower operating positions) within the shaft assembly 54.

The lower annular groove 105 carries a resilient annular seal, here anO-ring, 106. In the first, up position of the push rod 55 shown in solidlines in FIG. 5C, the O-ring 106 engages the upper part of the upperbore 59 of the cylindrical upper portion 63 of the shaft head 60 andcreates a vacuum-tight seal between the shaft assembly 54 and push rod55. The rod element 100 of the push rod 55 extends snugly but slidablydown into the rigid tube 61 of the shaft assembly. In this upperposition of the push rod, its upper annular groove 104 is exposedimmediately above the top of the handle 70, which is flush with orextends slightly above the tops of the fingers 73. More particularly,the top of the handle 70 in the portion thereof surrounding the fingers73, is formed by an upstanding annular projection 110 (FIGS. 3, 5A and6) upstanding from the major length of the handle 70 and defined by aradially outwardly extending annular flange 111 overlying a coaxialannular groove 112.

A retaining clip 113 is, in the preferred embodiment shown, used to lockthe push rod 55 in its upper position shown in solid lines in FIG. 5C,during mixing and prior to loading of the mixed cement downward into thecartridge 12. The clip 113 here comprises a platelike body 114 (FIG. 6)of any convenient shape to be gripped by the fingers of the user. Theleftward (FIG. 6) end of the platelike body 114 has a depending portionforming a leftward opening boxlike rectangular cross section sleeve 116integral with and depending from the plane of the body 114. Notches 115and 117 open leftward from the upper and lower walls of the boxlikesleeve 116 so as to allow the upper and lower walls of the boxlikesleeve 116 to be leftwardly received in the annular grooves 104 and 112respectively in the push rod 55 and handle annular projection 110, tothereby engage in the retainer clip notches 115 and 117 the material ofthe push rod 55 and handle 70. With the retainer clip 113 thus in place,as shown in solid lines in FIG. 5C, the push rod 55 cannot be pusheddownward out of its upper position shown nor be inadvertently pushedupwardly to unseat the O-ring resilient vacuum seal 106. Pulling theretainer clip 113 rightwardly (FIG. 5C) out of contact with the push rod55 and handle 70 allows the push rod 55 to be pushed downward by theoperator out of its position of FIGS. 3 and 5C and into its lowerposition of FIG. 4. Thus, after mixing is completed and it is desired toallow the push rod to be moved downward to its lower position in FIG. 4,the operator merely grips the clip 114 in his fingers and pulls sameradially out of engagement with the push rod 55. The push rod 55 is thenfree to be pushed downwardly farther into the shaft assembly into itslower position of FIG. 4.

The funnel 30 (FIGS. 3 and 3A) has a cylindrical outlet portion 120integrally and coaxially dependent from the bottom of the conicalportion 31. The bottom of the mixing chamber 11 is a threaded connectorsleeve 121 which integrally and coaxially depends from the cylindricaloutlet portion 120, is radially enlarged from the cylindrical outletportion 120 and has internal threads 122 (FIG. 3A). The threadedconnector sleeve 121 at its top integrally connects to the coaxial,smaller diameter cylindrical outlet portion 120 by a radially inwardextending flange 123.

As seen in FIGS. 2 and 3, the cartridge 12 comprises a hollow tube 124,open at its upper and lower ends, and provided at its lower end with aradially outwardly extending flange 125 for removable connection to agunlike cement ejector (not shown). Various types of gunlike cementejectors are known and a preferred one is disclosed in correspondingU.S. application Ser. No. 07/769 003, pending assigned to the assigneeof the present invention. The flange 125 can thus be called a gun mountflange. The cartridge 12 also has a radially inwardly extending flange127 (FIG. 4) at the bottom of the tube 124.

The upper end of the cartridge tube 124 is externally threaded at 126.The external threads 126 serve two purposes.

First, during loading of the cartridge 12 with mixed cement, ashereafter discussed, the threaded upper end 126 of the cartridge tube124 is fixedly but releasably coaxially threaded up into the internalthreads 122 of the threaded connection sleeve 121 and against the flange123, to fix the cartridge 12 to the bottom of the mixing chamber 11 forfilling with cement mixture. The interior walls of the funnelcylindrical outlet portion 120 and cartridge tube 124 are of the samediameter and axially abut, so as to axially smoothly continue one intothe other without discontinuity, for smooth filling of the cartridgewith mixed cement from the funnel.

The second purpose served by the threads 126 on the top of the cartridge12 is to threadedly receive, after the cartridge 12 is filled withcement mixture and removed from the mixing apparatus 10, the internallythreaded end 130 of a cement injection nozzle of any convenient type andrepresented in FIG. 2 by way of example at 131. It will be understoodthat a variety of injector nozzles 131 can be fitted to the threaded end126 of the cartridge 12.

If desired, the exterior surface of the cartridge 12 can be providedwith axially extending and/or circumferentially extending reinforcingribs, not shown, to reinforce the cartridge against internal pressureapplied to the mixed cement therein during dispensing into a surgicalsite.

A piston 140 (FIGS. 2, 3 and 3A) here comprises a 10 circular, hockeypuck-shaped member comprising an upwardly concavely curved top 141 (FIG.3A) having a relatively narrow central depression 142. The diameter ofthe depression 142 somewhat exceeds the diameter of the bottom of therod element 100 and is adapted to receive the latter therein ashereafter discussed, for piloting the bottom of the shaft assembly 54with respect to the piston 140 and mixing chamber 11. The piston 140further includes a substantially cylindrical peripheral wall 143depending from the periphery of the top 141 and an annular cylindricalreinforcing flange 144 depending from the top 141 in radially spacedrelation between the depression 142 and peripheral wall 143. The upperportion (for example the upper 1/4 to 1/3) of the piston peripheral wall143 is separated from the central portion of the piston 140 by a narrow,upfacing annular groove 145 and thereby forms an upstanding and somewhatradially outwardly biased annular feather seal 146. The annular featherseal 146 pushes radially outward against, and thus seals against, thesurrounding internal cylindrical surface of the lower end portion of thefunnel 30 in the upper position of the piston shown in FIG. 3A. It willbe understood that the upstanding annular feather seal 146 similarlybears resiliently and sealingly against the interior surface of thecartridge tube 124 after the piston has been pushed down into thecartridge 12 (see for example FIG. 4), as hereafter described.

The downward and radially outward pressure of fluid cement componentsand mixed cement, against the top of the piston 140, presses the featherseal 146 even more firmly radially out against the surrounding interiorwalls of the funnel bottom portion and (later) the cartridge tube, tofurther improve the effectiveness of the feather seal 146. Nevertheless,the orientation of the feather seal 146 allows it to slide easilydownward, in a wiping manner, along such surrounding walls, without anytendency to catch or snag, so as not to interfere with easy downwardsliding of the piston 140.

The piston 140 is initially positioned in its FIG. 3A position, namelyin the cylindrical outlet 120 of the mixing chamber 11. The piston 140is resiliently held in this position by a resilient detent herecomprising an annular bead 150 radially inward extending from theinterior face of the outlet 120, which bead 150 snaps into acorrespondingly shaped outwardly opening annular groove 151 in thebottom half of the cylindrical sidewall 143 of the piston 140. In thisposition, the piston 140, with its peripheral feather seal 146, plugsthe bottom of the mixing chamber 11 prior to and during mixing so thatthe cement components cannot escape from the funnel 30 downward into thecartridge 12. On the other hand, after mixing is completed, a modestdownward pressure, manually exerted by the user on the push rod 55,overcomes the resilient detent at 150, 151 and displaces the piston 140downward past the flange 150, out of engagement with the funnel 30 andinto the top of the cartridge tube 124. The bead 150 and groove 151 haveradially inward and downward sloped top surfaces which cooperativelyblock accidental dropping of the piston 140 during mixing but allowintended downward displacement of the piston by the user. This geometrythus facilitates the transition of the piston from the seat in the bowldown into the cartridge. On the other hand, the bead 150 and groove 151have bottom portions with a square edge which prevents the piston frommoving upwards. The square edge greatly increases the force required tovertically move the piston upward. Therefore, force required to move thepiston vertically upward is greater than the force to move the pistonvertically downward.

The bottom outer edge of the piston 140 is preferably chamfered at 152to facilitate downward motion of the piston into the outlet portion ofthe mixing chamber 11 and thereafter into the cartridge 12.

The horizontal wall 46 of the lid 45 at a location spaced laterally fromthe hub 52, spokes 53 and perimeter flange 50 is provided with a smallthrough hole 155 (FIG. 3B) which is normally covered and sealed by avacuum release label 156.

In general, the components of the above-described apparatus 10 are ofsuitable rigid plastics materials. The piston 140 is preferably ofmolded high density polyethylene with a thin enough cross section in itsannular feather seal 146 as to allow resilient inward bending thereof bythe surrounding lower cylindrical portion 120 of the funnel as to createa seal therebetween as seen in FIG. 3A. The rigid tube 61, auger 81 andrivets 97 are preferably of stainless steel. The annular seals 25 and 51are of a conventional resilient material, such as rubber or neoprene, asare the O-rings 65 and 106 (FIG. 6) which seal between the lid 44, shaftassembly 54 and push rod 55. The vacuum release label 156 is a pliable,adhesive tape-like member.

OPERATION

The apparatus 10 is intended to mix a two-part bone cement under apartial vacuum and, continuing under the same partial vacuum, todisplace the mixed cement into a dispensing cartridge atop a pistontherein for subsequent ejection from the cartridge e.g. into the openedtop of a femur prior to inserting the stem of a hip joint replacement.

The lid assembly 44 can be assembled as follows. The upper portion 63(FIG. 5A) of the shaft assembly 54 is inserted up through the hub 52 ofthe lid 45 until the shaft flange 66 abuts the bottom of the lidhorizontal wall 46. The O-ring 65, in the shaft groove 64, thus forms avacuum seal with the interior of the lid hub 52. Thereafter, theradially inner end of the crank handle 70, with its upstanding annularprojection 110, is snapped over the fingers 73 at the upper end of theshaft upper portion 63 to axially lock together the handle 70, shafthead 60 and lid 45. The handle 70 will receive the upper end of theshaft assembly only with the corresponding sets of flats 76 and 77opposed so that rotation of the handle 70 positively rotates the shaftassembly. The preassembled shaft assembly includes not only the head 60,but also the depending tube 61 and rotor 62 with its auger 81 and paddle82 (FIG. 3).

The push rod 55, with the O-ring 106 installed in its lower annulargroove 105, is dropped down into the open top of the shaft assembly 54.More particularly the depending rod element 100 is dropped down into theopen top of the shaft assembly 54, through the bore 59 and tube 61. Theshank 102 of the push rod 55 (FIG. 5C) is pushed downward into the shaftupper bore 59 to the groove 104, leaving the latter exposed. Theretainer clip 113 is installed in its upper annular groove 104 of thepush rod 55 and in the annular groove 112 (FIG. 5C) of the upwardannular projection 110 at the radially inner end of the handle, thusblocking further downward entry of the push rod 55 into the shaftassembly 54. In this position, the push rod O-ring 106 bears sealinglyagainst the surrounding upper shaft bore 59 to effect a vacuum sealbetween the push rod 55 and shaft assembly 54. Also in this position,the bottom end of the rod element 100 is exposed to a small extent belowthe shaft assembly, to an extent that will leave it close spaced abovethe depression in the top of the piston 140, as shown in FIG. 3.

The piston 140 is dropped down through the open top of the funnel 30 andpushed down into the cylindrical outlet portion thereof until theannular bead 150 snaps into the annular groove 151 in the piston so asto fixedly close the bottom of the mixing chamber 11. The annularfeather seal 146 seals against the cylindrical interior wall at thebottom of the funnel 30 as seen in FIG. 3.

A cartridge tube 124 (FIG. 3) is threaded at its upper end into thethreaded connector sleeve 121 at the bottom of the funnel 30 in a snugmanner.

The joined funnel 30 and cartridge 12 are dropped downward onto the opentop of the vacuum shroud 13, with the cartridge 124 loosely entering thecylindrical casing 20 of the vacuum shroud and the funnel radial flange32 resting atop the seal ring 25 which in turn rests atop the upfacingradial flange 24 at the top of the vacuum shroud 13.

The cement components are poured into the open top end of the funnel 30.A typical bone cement is, for example, an acrylic cement comprised of aliquid monomer and a solid polymer. The solid polymer contains thereaction initiator and is typically a finely divided powder. When themonomer contacts the polymer a reaction ensues that polymerizes themonomer and cross-links the polymer into a high molecular weightpolymeric material. Either the liquid monomer or solid particulatepolymer can be added first. The piston 140 in its FIG. 3 positionprevents leakage of either downward out of the bottom of the funnel 30and into the upstanding cartridge tube 124. In the following discussion,it is assumed, by way of example, that the liquid monomer is added firstand thus pools atop the piston 140 in the bottom of the funnel 30.

Once both components of the cement have been dropped into the top of thefunnel 30, the lid, now carrying the shaft assembly 54 and push rod 55,is placed atop the top flange 42 of the mixing chamber 11 (FIG. 3), withthe O-ring 51 axially interposed therebetween for vacuum sealingtherebetween. Such locates the lower portion of the shaft assembly 54,notably the tube 61, auger 81, paddle 82 and base 83, within the conicalportion 31 of the funnel 30, the base 83 and push rod bottom end lyingslightly above the piston 140.

At this point, the vacuum source VS can be turned on, or connected tothe stub 37 (FIG. 3). The vacuum source draws air and other gases fromthe interior of the funnel 30, through the hole 43 in the flange 42, andfrom inside the lower portion of the cartridge tube 124 and within thevacuum shroud cylindrical casing 20 upward through the depression 27 andthe lower portion of passage 36, so as to place these areas under apartial vacuum (subatmospheric pressure). The filter 40 absorbs noxiousreaction gases from mixing of the cement components and drawn from themixing chamber 11. Atmospheric pressure outside the apparatus 10, beinggreater than the partial vacuum in the interior of the funnel 30 andwithin the vacuum shroud 13, presses the lid 45 and the top of thevacuum shroud 13 in tight axially sandwiching relationship against theannular seals 51 and 25 and therethrough against the top and bottom endsof the funnel 30 to block air leakage into the interior of the funnel 30and vacuum shroud 13 so as to maintain a partial vacuum therein duringmixing of the cement components. This pressure difference, between thehigher outside atmospheric pressure and the lower inside subatmosphericpressure (partial vacuum), rigidly fixes axially together the lidassembly 44, the mixing chamber 11, and vacuum shroud 13, without needfor any other fastening means, and to the extent required to enablemixing of the cement and loading of the mixed cement into the cartridgeas hereafter discussed in more detail. The O-rings 65 and 106 maintain avacuum seal between and prevent air leakage between the lid 45, shaftassembly 54 and push rod 55.

In the embodiment shown, the apparatus will maintain a partial vacuum ofabout -22 inches of mercury therein which substantially preventsincorporation of air into the mixture during mixing and transfer to thecartridge.

The operator can now rotate the handle 70 (FIG. 3) in either or bothdirections (clockwise and counterclockwise) to start mixing of themonomer and polymer. When the monomer and polymer are mixed underpartial vacuum, as here, the void volume of the resultant high molecularweight polymeric material is considerably less than when mixed in air atatmospheric pressure.

The conical funnel geometry of the funnel 30 minimizes edges anddiscontinuities in the flow stream lines of the cement as it is beingmixed. Since the object of the mixing and transfer device embodying theinvention is to minimize voids and pores in the resultant cementmixture, any discontinuities in the stream lines of the mixture duringthe transfer operation could cause turbulence or eddies. Therefore,voids or pores could be introduced into the cement mixture at suchdiscontinuities. Accordingly, this problem is avoided by thefunnel-shaped geometry of the mixing chamber 11.

During mixing, the flexible auger 81 contacts the inside surface of theconical funnel 30 along its outermost edge as it rotates about thecentral axis of the bowl. The auger 81 serves two purposes. First,during the mixing operation, if rotated top edge leading (here clockwiseseen from above), the auger moves cement from the upper region of thecone-shaped funnel 30 down into the lower region of such funnel. Theauger thus continuously brings down powder loose in the upper portion ofthe funnel 30 down into contact with the mixture at the bottom of thefunnel. The highest concentration of the liquid monomer (particularlywhen the monomer is put into the funnel first) may be at the bottom ofthe funnel 30. The highest concentration of the powder, which isrelatively lightweight, may be expected in the upper region of thefunnel 30, particularly when the powder is added to the funnel after theliquid monomer. Therefore, the auger aids the mixing process bycontinuously moving powder downward into the highest concentration ofmonomer. Second, during the transfer operation hereafter described, theauger moves the mixture off the conical sidewall 31 of the funnel 30 andout the bottom of the funnel 30 into the open top of the cartridge 12.

During mixing, the auger 81 and paddle 82 cooperate in a unique manner.The springy metal auger 81 at its radially outermost edge attacks theconical sidewall 31 of the funnel 30 during mixing and wipes materialoff it. The paddle 82 maintains a gap, for example between 1/8 inch and1/4 inch, radially in from the conical sidewall 31 of the funnel 30 andthereby spreads a thin film of cement and cement components along theperipheral conical wall 31 of the funnel 30. The thin film is created tofurther assist in deaerating the cement, take the air out of it, byreason of exposure of the surface of this thin film to the partialvacuum within the funnel 30. The auger 81 thereafter rotatably scrapesthat thin film of cement material back down into the center of the mix.The auger continues to tend to keep moving the highest concentration ofpowder down into the highest concentration of monomer in the mix.

The central opening 95 (FIG. 3) in the auger 81 provides additionaledges to contact the cement materials to be mixed and help mix same. Thecentral opening 95 also allows the auger 81 as a whole to be more easilyflexed and to conform at its outer edge 91 more closely to the innerface of the conical funnel sidewall 31 during mixing and transfer.

It is important that the feather seal 146 of the piston be effective toallow the piston to form a positive blockage at the bottom of the mixingfunnel 30 since otherwise the monomer liquid would tend to run down intothe bottom of the cartridge, prior to mixing, and perhaps even into thebottom of the vacuum shroud, thereby preventing proper mixing andproduction of a proper bone cement.

It is important that, during mixing, the piston be kept in its uppermostposition shown in FIG. 3A and FIG. 3 by the retention or detentstructure shown at 150, 151 in FIG. 3A. With the piston thus held in aposition closing the bottom of the conical sidewall 31 of the mixingfunnel 30, the solid and liquid components to be mixed are kept withinthe funnel 30. This keeps the cement components to be mixed in contactwith the paddle 82 and auger 81 by which they are mixed and also keepssuch components facing upward into the partial vacuum in the funnel overa wide surface area, much wider than would be possible if the componentswere mixed within the cartridge 12, so as to increase the opportunityfor deaeration at the top surface of the mixture.

Using the funnel-shaped mixing chamber 11 here disclosed, it is possibleto make larger batches of bone cement than has normally been the case inthe past. A typical conventional cement batch is about 60 grams and themixing chamber 11 of the present invention handles easily 3 times that,the total volume of the mixing chamber 11 being about 550 cubiccentimeters.

After a minute or two of initial mixing, the mixed cement is theconsistency of thin pancake batter. The mixing time is typically 30 to90 seconds whereupon the mixture is transferred down into the cartridge.

After sufficient mixing, the mixed cement is transferred down to thecartridge 12 as follows. First, the operator radially pulls outward theretaining clip 113, out of contact with the push rod 55 and handle 70.This unlocks the push rod 55 and allows the operator to manually push itdownward from its FIG. 3 to its FIG. 4 position. The thus downwardmoving bottom of the rod element 100 (FIG. 3A) will, after a slight lostmotion, contact the top of the piston 140 (here at the upward facingsurface of the depression 142, overcoming the detent 150, 151 (FIG. 3A)and downwardly displacing the piston almost entirely out of the bottomend of the mixing chamber 11 and entirely or almost entirely into theopen top end of the cartridge tube 124.

Again then, after a minute or two of mixing, the cement is typically inthe form of a heavy but quite flowable, syrup-like or thin batter-likeliquid. Such liquid by its weight tends to push the piston 140 downfurther in the cartridge 12. Such gravitational transfer of the mixedliquid cement downward into the cartridge is assisted by operatorrotation of the handle 70 in a direction such that the top edges 93 and94 of the auger 81 and paddle 82 circumferentially advance ahead of thebottoms thereof (the auger 81 and paddle 82 being tilted as seen inFIGS. 5 and 5B). The auger 81 and paddle 82 thus tend to wedgedownwardly the portions of the mixed cement lying directlycircumferentially ahead thereof as they rotate in the funnel 30. In anyevent, by means of gravity and this wedging action, the flowable mixedcement drops downward into the open top of the cartridge and displacesdownward the piston 140 from its intermediate dotted line position ofFIG. 4 toward and possibly (if enough cement is mixed) to its bottommostsolid line position of FIG. 4.

Downward escape of the piston 140 out of the bottom of the cartridgetube 124 is positively blocked by the internal flange 127 in the bottomof the tube 124. Note that both the mixing of the cement components andthe transfer of the mixture from the mixing chamber 11 into thedispensing cartridge 12 takes place entirely within a partial vacuum.This avoids incorporation of air into the cement mixture during mixingand also during transfer into the cartridge and so avoids unwantedporosity of the cement.

The vacuum release label is most easily an adhesive bottomed paper orplastic film tape like a conventional household adhesive tape, whichsticks to the top of the lid horizontal wall 46 and blocks the hole 155thereby preventing leakage of air into the interior of the apparatusthrough such hole.

On the other hand, when mixing is completed and the mixture has beentransferred into the cartridge 12, filling the cartridge and pressingthe piston 140 down to its bottom FIG. 4 position, such that it is nowdesired to remove the filled cartridge from the apparatus 10, the tapeor label 156 can be manually lifted off the lid 45 and discarded,allowing air to bleed through the hole 155 in the lid and return themixing chamber 11 and vacuum shroud 13 and cartridge 12 to atmosphericpressure in the interior thereof. At the same time vacuum source VS canbe disconnected from the apparatus, as by disconnecting the vacuum tube38 from the stub 37 on the mixing chamber 11.

With the vacuum thus released, the mixing chamber 11 can then be liftedoff the top of the vacuum shroud 13, drawing up with it the filledcartridge 12. The top of the cartridge can then be unscrewed from thethreaded connection sleeve 121 at the bottom of the mixing chamber 11and the mixing chamber 11 can be discarded. The vacuum shroud 13 can beretained for later use with a new mixing chamber 11, etc. for mixing anew batch of cement at some time in the future.

The filled cartridge 12 (FIG. 2) can then have a suitable output nozzle131 threaded on the threads 126 at the upper end thereof and thecartridge as a whole, with nozzle 131, can be mounted on a gun (notshown) of the kind above discussed, to advance the piston away from theflange 125 and toward the threads 126 to press the mixed cement throughthe nozzle 131 into a desired bone cement location, such as, forexample, the upper end of a femur where injected cement is to receiveand fixedly hold in place the lower tang of a conventional hip jointreplacement.

Although a particular preferred embodiment of the invention has beendisclosed in detail for illustrative purposes, it will be recognizedthat variations or modifications of the disclosed apparatus, includingthe rearrangement of parts, lie within the scope of the presentinvention.

The embodiments of the invention in which an exclusive property orprivilege is claimed are defined as follows:
 1. An apparatus for mixingbone cement and containing the mixed bone cement preparatory todispensing, the apparatus comprising:a mixing chamber having a centralaxis and an inner surface and an outlet for outputting mixed cement; acartridge having means defining an inlet releasably coupled to theoutlet of said mixing chamber for receiving mixed bone cement therefrom;means for moving cement from an upper region of said mixing chamber downinto a lower region thereof to mix such cement and for moving such mixedcement off said inner surface of said mixing chamber and into saidcartridge, said means for moving including an auger mounted for rotationabout the central axis of the mixing chamber and a central shaftrotatably mounted in said mixing chamber and a paddle fixed on saidcentral shaft, said auger comprising a resilient plate having a bottomfixed to said central shaft, said auger having a radially inner edgeparallel to and spaced radially from said central shaft and a radiallyouter edge diverging upward away from said central shaft, the center ofsaid auger having a central opening of shape corresponding to the outerperimeter of said auger, said paddle having radially inner and outeredges respectively adjacent said central shaft and spaced radially fromthe inner surface of said mixing chamber.
 2. The apparatus of claim 1 inwhich said auger is flexible and said outer edge contacts the innersurface of said mixing chamber.
 3. The apparatus of claim 1 in whichsaid auger is fixed on said central shaft for rotation about saidcentral axis, said paddle being circumferentially offset from saidauger.
 4. An apparatus for mixing bone cement and containing the mixedbone cement preparatory to dispensing, the apparatus comprising:a mixingchamber having a central axis and an inner surface and an outlet foroutputting mixed cement; a cartridge having means defining an inletreleasably coupled to the outlet of said mixing chamber for receivingmixed bone cement therefrom; means for moving cement from an upperregion of said mixing chamber down into a lower region thereof to mixsuch cement and for moving such mixed cement off said inner surface ofsaid mixing chamber and into said cartridge, said means for movingincluding a central shaft rotatably mounted in said mixing chamber, anauger and a paddle, said auger and paddle being fixed on said centralshaft and mounted for rotation about said central axis, said mixingchamber being of frusto-conical shape extending from a narrow bottom toa substantially wider top, said paddle and auger having downwardlytapered, truncated bottom triangular shapes with the bottoms thereofadjacent the bottom of the conical mixing chamber, said auger beingapproximately twice the height of said paddle.
 5. An apparatus formixing bone cement and containing the mixed bone cement preparatory todispensing, the apparatus comprising:a mixing chamber having a centralaxis and an inner surface and an outlet for outputting mixed cement; acartridge having means defining an inlet releasably coupled to theoutlet of said mixing chamber for receiving mixed bone cement therefrom;means for moving cement from an upper region of said mixing chamber downinto a lower region thereof to mix such cement and for moving such mixedcement off said inner surface of said mixing chamber and into saidcartridge, said means for moving comprising a central shaft, said mixingchamber having a top, a lid closing said top of said mixing chamber androtatably supporting said central shaft pendently therefrom, a pistonaxially movably mounted adjacent the connection of said cartridge inletand mixing chamber outlet for movement coaxially thereof, and centralmeans on said piston and central shaft for piloting the bottom of saidcentral shaft with respect to said piston and with respect to saidmixing chamber.
 6. An apparatus for mixing bone cement and containingthe mixed bone cement preparatory to dispensing, the apparatuscomprising:a mixing chamber having a central axis and an inner surfaceand an outlet for outputting mixed cement; a cartridge having meansdefining an inlet releasably coupled to the outlet of said mixingchamber for receiving mixed bone cement therefrom; means for movingcement from an upper region of said mixing chamber down into a lowerregion thereof to mix such cement and for moving such mixed cement offsaid inner surface of said mixing chamber and into said cartridge, avacuum shroud surrounding said cartridge, said mixing chamber having abottom end, said shroud extending up substantially to said bottom end ofsaid mixing chamber, and means for connecting a vacuum source to theinterior of said mixing chamber and vacuum shroud to keep said mixingchamber and cartridge at a subatmospheric pressure during cement mixingand loading of the mixed cement into said cartridge.
 7. The apparatus ofclaim 6 in which said connecting means comprises a tube that connectssaid mixing chamber to said shroud, said tube being tapered and havingan opening at the shroud end which is smaller than its opening to themixing chamber, to allow said mixing chamber and cartridge to fill withair before the shroud.
 8. An apparatus for mixing bone cement andcontaining the mixed bone cement preparatory to dispensing, theapparatus comprising:a mixing chamber having an outlet for outputtingmixed cement; a cartridge having means defining an inlet releasablycoupled to the outlet of said mixing chamber for receiving mixed bonecement therefrom, said mixing chamber comprising means for minimizingedges and discontinuities in cement flow stream lines, said means forminimizing edges and discontinuities in cement flow stream linesincluding a funnel of downwardly converging conical interior shape, saidconical interior shape extending throughout the major height of saidmixing chamber, said mixing chamber interior having a bottom portionsmoothly continuing down from the bottom of said funnel and defining themixed cement outlet, said cartridge connecting coaxially to a bottom ofsaid mixing chamber bottom portion, said cartridge having the sameinside diameter as said bottom portion for smoothest cement mix flowdown into said cartridge.
 9. The apparatus of claim 8 in which saidmixing chamber comprises means for moving cement from an upper region ofsaid mixing chamber down into a lower region thereof to mix such cementand for moving such mixed cement off an inner surface of said funnel andinto said cartridge.
 10. An apparatus for mixing bone cement andcontaining the mixed bone cement preparatory to dispensing, theapparatus comprising:a mixing chamber having an outlet for outputtingmixed cement; a cartridge having means defining an inlet releasablycoupled to the outlet of said mixing chamber for receiving mixed bonecement therefrom, said mixing chamber comprising means for minimizingedges and discontinuities in cement flow stream lines, said means forminimizing edges and discontinuities in cement flow stream linesincluding a funnel of downwardly converging conical shape, said mixingchamber having an interior shape of said conical shape throughout themajor height of said mixing chamber; said mixing chamber having a bottomend, means for preventing incorporation of air into the cementcomprising a vacuum shroud surrounding the cartridge and extending upsubstantially to the bottom end of the mixing chamber and means forconnecting a vacuum source to the interior of said mixing chamber andvacuum shroud to keep the mixing chamber and cartridge at asubatmospheric pressure during cement mixing and loading into saidcartridge.
 11. An apparatus for mixing bone cement and containing themixed bone cement preparatory to dispensing, the apparatus comprising:amixing chamber having an outlet for outputting mixed cement; a cartridgehaving means defining an inlet releasably coupled to the outlet of saidmixing chamber for receiving mixed bone cement therefrom, said mixingchamber comprising means for minimizing edges and discontinuities incement flow stream lines, said means for minimizing edges anddiscontinuities in cement flow stream lines including a funnel ofdownwardly converging conical shape, said mixing chamber having aninterior shape of said conical shape throughout the major height of saidmixing chamber, said mixing chamber comprising an open topped,downwardly converging funnel with a radially outwardly extending topflange, said mixing chamber further comprising a horizontal lid and anannular seal separating said lid from said top flange and creating avacuum seal therewith, means for connecting said mixing chamber to avacuum source comprising a passage outside said mixing chamber andopening up through said radially outward extending top flange of saidmixing chamber at a location radially inboard thereof, the top of saidpassage being spaced below said lid for communication between saidpassage and the interior of said mixing chamber.
 12. An apparatus formixing bone cement and containing the mixed bone cement preparatory todispensing, the apparatus comprising:a mixing chamber having an outletfor outputting mixed cement; a cartridge having means defining an inletreleasably coupled to the outlet of said mixing chamber for receivingmixed bone cement therefrom, said mixing chamber comprising means forminimizing edges and discontinuities in cement flow stream lines, saidmeans for minimizing edges and discontinuities in cement flow streamlines including a funnel of downwardly converging conical shape, saidmixing chamber having an interior shape of said conical shape throughoutthe major height of said mixing chamber; means for mixing cement in saidmixing chamber including a rotatable shaft extending down into saidmixing chamber in which said shaft is hollow, a push rod sealingly andvertically moveable in said hollow shaft, a piston moveable down in saidcartridge by downward movement of said rod for loading mixed cement fromthe mixing chamber down into said cartridge.
 13. The apparatus of claim12 in which said cement moving means further comprises a handle securedto said shaft by a snap fit connection.
 14. An apparatus for mixing bonecement and containing the mixed bone cement preparatory to dispensing,the apparatus comprising:an upstanding mixing funnel having a centralaxis and tapered frustoconically downward to a bottom outlet foroutputting mixed cement; a cartridge having a top inlet releasablycoupled to the bottom outlet of said mixing funnel for receiving mixedbone cement therefrom; means for moving cement from an upper region ofsaid mixing funnel down into a lower region thereof to mix said cementand for moving such mixed cement off an inner surface of said mixingfunnel and into said cartridge, said means for moving including acentral shaft rotatably mounted in said mixing funnel for rotation aboutthe central axis of said mixing funnel, an auger and a paddle fixed onsaid central shaft and circumferentially offset from each other, saidauger and paddle being inclined upward and in opposite directions awayfrom a diametral plane of said central shaft for rotation with their topedges leading or assisting downward movement of cement in said mixingfunnel, said auger and paddle differing in shape and size and purpose,said inclined paddle being rigid and having an outer edge spaced fromthe inner surface of said mixing funnel for spreading a layer of cementon the inner surface of said mixing funnel, said inclined auger being ofthin springy sheet material and having a correspondingly inclined outeredge portion which elastically bends curvilinearly to substantiallyconform to, and bear slidably against, the funnel inner surface to wipecement off said mixing funnel inner surface and down into saidcartridge.
 15. The apparatus of claim 14 in which said auger isframelike with perimeter portions surrounding an open central window andthereby providing additional cement mixing edges, said auger extendingsubstantially the full height of said mixing funnel and well above theheight of said paddle.